The blade holding nut torque specification for the D160 is 65 ft-lbs (according to the manual). Since the sheave pulley is at the opposite end of that spindle, I would say that it is also 65 ft-lbs, BUT I only tighten mine to 50 ft-lbs since the portion of the spindle at that end is somewhat smaller than at the blade end and it is easy to check for looseness before operation. I tighten the four self-tapping screws that hold the spindle to the cutter deck to 23 ft-lbs. (because the 8 x 1.25 10mm screws are only rated for 24 ft-lbs of torque according to the metric torque charts). So far so good. I've been operating this mower weekly for the past 4 years. It has 284 hours on it as of yesterday.